The measurement of portions of granulated compounds is a critical process in a wide range of manufacturing processes. As an example, without limiting the application of the present disclosure, in the manufacture of small arms ammunition cartridges, precise propellant loads are required to ensure that projectiles (bullets) are accelerated consistently. The prior art discloses various methods to measure the volume of propellant prior to being loaded into cartridge cases. Although the prior art also teaches several different methods of measuring the weight of portions of granules, the methods are either too slow or too inaccurate to be practically applied to the high speed mass production of precision small arms ammunition.
The size and density of propellant granules vary with each manufactured batch or “lot” of propellant. At present the density of each granule of propellant can vary by as much as 16%. Contributing factors to the variability of propellant lots include the temperature and humidity of the environment at the time propellant granules are manufactured, shipped, and handled; minute variations in the calibration of the equipment that determines the size of each granule; statistically anomalous granulation; and other factors. While volumetric measurement of spherically shaped propellant can be accurate to within one tenth of a grain (0.000229 ounces) of propellant granules of the same lot, because the size and specific density of granules in different lots is inconsistent, portions of measured propellant, and the specific impulse imparted when the propellant is fired, is significantly inconsistent from lot to lot. Moreover, ammunition propellant granules are designed in several different varieties of shapes and sizes for use with various types of cartridges and in various types of firearms. Non-spherical shapes and larger sizes are less accurately measured by volumetric means alone.
Additionally, the metering system should be capable of feeding the cartridge loading process at a rate consistent with the speed with which automatic cartridge loading apparatus are capable of assembly. Depending on the size and shape of cartridges being loaded, the speed with which modern cartridge loading systems operate can exceed 240 units per minute. Generally, the speed of production is constrained by the speed with which propellant can be apportioned and deposited into ammunition cartridge cases during assembly.
The prior art teaches various means of mechanically producing portions of granules. Whereas these processes may be reasonably accurate in the uniform portioning of spherical granules, volumetric measurement of granules that are not spherical in shape produce inconsistent results because the volume such granules occupy is affected by the position of the granules within the volume. As an example, granule flakes, as well as elongated cylindrical forms called “stick” granules, may either be randomly oriented or stacked. The density, and therefore the weight, of a small volume of flake or stick granules can significantly vary depending on the orientation of the granules within the volume of measurement.
Additionally, the most accurate methods of mechanically producing portions of granules by volume disclosed in prior art involve techniques such as worm screws and various methods of volume isolation by means of the movement of hard-edged volumetric capsules relative to hard-edged granule feed source tubes or troughs. These mechanical methods have a tendency to crush or slice non-spherical granules such as flake and stick shaped granules. Crushing and slicing propellant granules results with burn rate variations and inconsistency in the rate of acceleration of projectiles. This results with undesirable and inconsistent barrel pressure, projectile acceleration, muzzle velocity, and thereby accuracy, when ammunition is fired.
Military personnel are trained to select ammunition of the same lot where accuracy of fired projectiles is considered mission critical. By selecting ammunition of the same lot, it is assumed that each lot of ammunition contains the same lot of manufactured propellant material. Using a particular manufactured lot of spherical propellant material, the prior art can obtain volumetric measurement accuracy to within ten percent (10%) of a grain (0.000229 ounces) of each successively measured portion of granules. Since the specific density of a volume of propellant varies widely by manufactured lot, using the same volume to measure a different lot of propellant results with significant deviation between manufactured cartridges. However, volumetric measurement of various shapes of granules can be widely inconsistent. The volumetric measurement of flat or “flake” propellant, or elongated cylindrical forms, called “stick” propellants, are significantly less accurate by volume than spherical granules, called “ball” propellants. The shape of propellant granules is a critical design attribute of the propellant affecting the rate of burn and thereby the internal ballistics of ammunition when fired. The physical shape of propellant granules is a preferred means of regulating the internal pressure and the specific impulse imparted by during the propellant burn.
Moreover, the mass production of harmonically resonant ammunition, which in the best instance differentiates minutely precise variations in the weight of portions of propellant loads to a resolution of individual granules of propellant, the specific weight of propellant of various classes of harmonic loads necessitates that the granule metering system be capable of adjustment so as to consistently conform production to the specifically desired weight of propellant. It is well known that harmonically resonant or “tuned” ammunition, when matched to specific individual rifles, can more than double the accuracy of fired projectiles. However, because harmonically resonant ammunition requires precise portions of propellant measured to consistently match the rate of projectile acceleration with the harmonic properties of individual rifles, cost effective mass production of such ammunition has not been practicable. The present invention enables the mass production of such harmonically resonant ammunition by providing not only for more accurate measurement of propellant by weight, but also by enabling the automatic adjustment of portions of propellant to accurately differentiate between a range of propellant load classes so that users can reliably select the class that is most accurate when used with a particular rifle.
The most accurate way to measure granulated compounds is by weight. The accuracy of measurement and portioning by the present invention is consistent regardless of variations in the size, shape, density, and the volume of aggregates of various lots of granules of the same chemical or compound. In the production of ammunition propellant loads, provided that isolated portions of propellant do not contain crushed or sliced granules, the specific impulse, rate of burn, and internal ballistic pressure curves are most consistent.